Parasites and Pathology in Three Endemic Marine Invertebrates Under Salmon Farm‐Derived Organic Enrichment

As aquaculture expands, a deeper understanding of its ecological implications, particularly those associated with organic enrichment, is needed. Marine filter‐feeding invertebrates serve as ecosystem engineers, nutrient cyclers and trophic intermediaries and are essential to maintaining water quality. However, their physiological responses, host–parasite interactions and reproductive biology under stress are poorly understood. New Zealand scallops ( Pecten novaezelandiae ), horse mussels ( Atrina zelandica ) and brachiopods ( Neothyris lenticularis ), which are endemic to Aotearoa New Zealand, were exposed to controlled laboratory and in situ organic enrichment regimes designed to simulate organic loading associated with finfish aquaculture. Their responses were explored using histopathological techniques. Several parasites and tissue conditions were detected, with some showing variability across organic enrichment levels. For instance, in A. zelandica , a higher prevalence of Endozoicomonas ‐like organisms (ELOs) was observed under enrichment, and an unidentified parasite was linked to haemocyte infiltration. Pecten novaezelandiae showed a lower prevalence of ELOs in enriched treatments, and some individuals exposed to lower enrichment conditions exhibited digestive gland tubules without digestive epithelial virosis. No parasites were observed in N. lenticularis , but subtle changes in ceroid accumulation in relation to organic enrichment were observed. The insights gained from this research establish an initial foundation for understanding benthic invertebrate health in relation to environmental stressors and highlight the importance of considering host physiology and host–parasite–microbiome dynamics within an ecosystem‐based aquaculture management framework.